Apparatus for wear indicating and logging while drilling



Nov. 13, 1951V v E. A. JOHNSON APPARATUS FOR WEAR INDICATING AND LOGGING WHILE DRILLING 2 SHEETS-SHEET l Filed Feb. 27, 194'? NN N SSN ln ven o r'- Nov. 13, 1951 E. A. JOHNSON 2,575,173

APPARATUS FOR WEAR INDICATING AND LOGGING WHILE DRILLING E vere# 'A Johnson Patented Nov. 13, 1951 APPARATUS Foa WEARINDICA'IING AND LoGGING WHILEy DRILLING Everett A. Johnson, Park Ridge, Ill.. assignor to Standard Oil Company, Chicago, Ill.,v a corporation of Indiana n Application February 27, 1947, Serial No. 731,242

(Cl. Z55-1) 4i Claims.

This invention relates to method and apparatus for transmitting information or indications of operating conditions-from an inaccessible point, for example from a bore hole to the surface oi the earth. More particularly, the invention pertains to method and apparatus for detecting well tool wear.

This invention has particular utility in connection with logging-while-drilling wells. `Dur ing the drilling of wells it is desirable to determine at least the approximate nature or characterfof the geological strata traversed and the invention includes means whereby the conductivity of strata traversed by a drill hole may be measured or indicated during the drilling operation. It also includes means for continuously measuring the natural potential in the region of the well. Y

In the rotary drilling of wells a drill bit is advanced'through the successive formations by the rotation of the drill stem, ya drilling fluid being circulated into and out of the well for the purpose of removing they drill cuttings, lubricating and cooling the bit, etc. Frequently, the drill iluid is repeatedly used in a substantially closed circuit kand is replenished only to the extent that it is absorbed by the penetrated formations, The formation through which the well is passed is subjected to the downward pressure and to the cutting and grinding action of av revolving metal bit. The hardness and density of the strata traversed determine the resistance to penetration and displacement and, in turn, determine the length of time a bit will be effective.

Two general types of bits are known in the art, one being the drag bit which is particularly adapte'd'to loosely-cemented sands, shales, and clays, and theother being the rock roller or cone bit which depends upon a crushing and chipping action. These bits are well `known and` widely used in oil field drilling. The'drag kbit wears on both the bottom and the side cutting edges;

VWhereas the rock bit failure frequentlyV occurs at the bearings upon which the cones orrollers are mounted. v

In operation the cutting bit usually is revolved by a hollow drill stem and at the surfacemeans are provided for rotating the drill stem and for supplying a drill fluid to the hollow Vdrill stem. The drill uid passes downwardlythrough the drill stem,'ilows out into the wellthrough the bit, sweeps under the bit, andsuspends thedrill cuttings `therein for transfer toy "the surface. When the fluid laden'with drill' cuttings reaches the surface, it is introduced'f'into 'a separating ditch or trough wherein the relatively coarse'ma.-v

terials are settled out. Alternatively thef drill mud can be passed over a shaker screen which retainsthe well cuttings. In any event, thedrilling fluid or mud from which the cuttings have been removed is introduced into an accumula' tion trough or sump from which it is pumped back into the well. A modification of the above operation is that which is termed reverse cir-Z culation. In such a system the drill fluids are pumped downwardly outside of the drill'stezn and are returned to thesurface through the drill stem. Y-

.If Vthe drill bit isv permitted to become dull as a result of wear or failure, the drilling rate and/or the well diameter willbe reduced. Even-.- tually` the drilling yratewill be reduced until further drilling withfthe lsame bit would not be economical. In passing from a relatively soft formation the drillingrate will also be reduced and it has not always been possible to distinguish between the possible causes for reduction in drill-.- ing rate. Consequently, drill `bits have been pulled prematurely. It is also possible that the nature of the formation through'which the bit is passing is such that th-e sid-e cutting edges of the `drill bit may alsor become worn without being de'- tected and the hole will be off gauge. Consequently, the problem becomes one of detecting the failure or extent. and character of the wear of a drill bit.` Y

'Drill bits are available at relatively'high costs l f Heretofore various means have been proposed proposed that a radioactive material be released into the well stream anddetected atthe surface by means of highly-specialized equipment-It extent that `they cannot be detected with con'- siderable accuracy and are considered to be unsatisfactory for the intended purpose... l

It is, therefore, an object of my invention to provide a. simple method and'means fortransmitting information or indications of certain conditions of apparatus within a well bore. It is a further object to provide a method-and means i for positively indicating, at the surface, the extent and character of wear of well tools-Within the well bore. Anotherggobject is to provide a well logging system whichautomatically indicat'es a predetermined extent of bit wears A further object is to provide a logging-whiledrilling-system wherein an electrical log is obtained and the condition of therbit is indicated electrically. These and other objects will become apparent as the description of my invention proceeds with reference to the' drawings wherein:

Figures land 2 arediagrammatic representations of drilling assemblies employing my indicator electrode means; Y Figure 3 is a schematic showing of a circuit adapted for logging-while-drilling and for indicating bit wear; and

Figure 4'is a diagrammatic representation of a drilling assembly for use with the circuit shown in Figure 3.

L, vReferring to Figures 1.2 and 4, the apparatus includes a drill bit I0, having bottom cutting edges II, and drill stem I2. The bit I may be provided with one or'more cavities I3 which extend inwardly from a wearing surface. An insulated electrode I4 is disposed within the cavity I3 and wear plug or shieldI5 `normally protects the electrode I4 Within the cavity I3 to a depth corresponding to the allowable wear; Thus, during the drilling operation the 'metalof the well tool and the shield I5 wear away, ,exposing the electrode I4 when a predetermined amount of wear has occurred. A threaded plug of insulating material can beused to shield the electrode I4 but other convenient plugging means may be substituted. The electrodes may be of any desired area or configuration so long as an electrical signal is transmitted to thelwear indicatingor well logging circuit.

In Figure 1 the drill bit I0 is provided with an insulated electrode I4 within cavity I3 enclosedby shieldY I5.l The electrode I4 is con'- nected to the electrically conducting drill stem I2 by conductor 22 at 23 and'insulator I6 is disposed between the drill I0 and drill stem I2.v A battery I'I and an electrical measuring instrument such as a' galvanometer I8 in series with electrode 2| and drillv stem I2 are provided 1at the surface. Normally'there is no Viiow of current'between the electrode 2I and the drill bit III but when the shield I5 is removed by the wearing of the drill bit, the electrode I4 is exposed and the circuit including indicating lelectrode I4 and the groundelectrodeZI is cornpleted.' Upon the completion of this circuit there is an indication at the surface by galvanometer Y I8 that the K predetermined extent of Wear has ocurred.; i .r Y.

`face which indicates that a Another embodiment of the invention is illustrated in Figure 2 wherein the indicating circuit includes the shielded electrode I4, the power source I'I and an electrical measuring instrumentV I8. In addition the conductors and 22 and electrode I4 comprise one portion of the circuit andthe conductor'IS, drill stem I2and bit I0 form another portion of the circuit. As before, when the shield I5 is removed, the circuit is "completed between the then exposed electrode I4 andthe drill bit L0 by the well fluid or formation therebygiving an indication of the predetermined extent of Wear.

' Thus, each of the embodiments illustrated in Figures Yl and 2 comprises a bit I0 provided with one or more insulated electrodes I4 which are electrically shielded-by plug I5 and which are connected by means of insulated conductors with an electrical measuring instrument at the surparticular electrode has become exposed. y n

If desired, two or more indicating electrodesV may be used on different portions of the well tool, guide shoe, and the like, so vthat it Will be possible to determine not only the extent but also the character of the wear, failure, or penetration. For example, if different indicating means are used on the bottom and side cutting blades of a drag bit, it is readily determinable whether continued drilling would result inv decreasing drilling rate or in reducinghole Vdiam-- eter. It is also contemplated that my indicating means can be employed on any type of Well tool or apparatus including drill pipe protectors, pins in roller bits, casing collars, reamers, vand the like tov indicate the failure, extent and character of wear, or penetration. f' f y,

With reference to Figure 3 I have provded'a combination logging and bit wear indicating circuit, which circuit is so integrated .that a mini-v mum of apparatus is required. The logging circuit comprises an A. C. portion for measuring the earth resistivity, which A. C. is rectified to a pulsating D. C. current supplied to a D. C.` recorder. The portion of the circuit for indicating bit Wear yis a D. C. circuit which is connected in parallel to the D. C. portion of the logging circuit. More specifically, alternating current generator 25 having a constant output is connected to a coupling transformer 29 by leads 21 and 28. Logging electrodes 3| and 32 are connected .through their respective leads 3Ia and 32a to the coupling transformer whereby a xed alternating potential is supplied across the electrodes. Electrode 32is'located at the base of the well being logged and may be, for example, the drill bit, and electrode 3I is an electrode located at the surface or in the well some distance from the first electrode 32. Variations in the resistivity of the earth surrounding electrode 3| or of the well fluids when both electrodes are in the Well will cause variations in the current flowing in lead 32a, which current variations are converted into a variable potential across a fixed resistance 34 in lead 3Ia. This varying A. C. potential is amplified in a suitable amplifier 35 and rectified in a full wave rectifier 36.- The pulsating D. C. output vof the full wave rectifier is then fed through lead 2I on one hand and leads 5I and 28 on the other to the recording portion of the'logging circuit. It should be particularly noted that by converting the variable potential across the logging electrodes into a D. C. potential, leads 21 and 28 which, as pointed out above are carrying A. C. potential-to the logging electrodes; may be .used without intel?,-

ammira leadsV 2 1 and! 8 to preventxthe D. (3.1 .from reaching 1. generator ...2.5, rand blocking` lmndenser.-A is rinsertedzin the circuitsimilarly to protect the coupling transformer .29. Choke .coils Y3l .inleads 21 and rziisimilarly preventA.-.C.. from reaching the rectifier .35,

The recording portion in the'loggingcircuit may-include a custo-mary D. C. indicatorl rsuch as an oscillograph galvanometer and la potential divider comprising a source of potentialsuchias a battery 40 across which is a variable resistance 42. The potential divider serves the purpose of permitting `the adjustment of the zerov point of the recorder. Choke coils 39 protect {the D. 'C. recorder from the A. C.fcurrent. YA recorder of 6 `ment the .ground electrode .3l .and :the fdril-ll bit in :correspond Lto the logging .electrodesystem .131

. fand- 32 :or .Figure 3. J Likewise,` the-*shielded .elect trodes 'I4 '1and..44- .correspond to the indicating electrode system .43--44.v Thereforaif the'. leads i3 ta,- 13211, 43a, and Y"44a of; Figure 3v were connected las f illustrated .in Figure 4, ztthe. apparatus 'would be :adapted rto loggingewhile-drilling :and in tate on' an/A.- C. potential'andthe drillnbit `wear this type will record the pulsating DVC. output of the full wave rectifier 36, in the .circuit as 'described, as a variation in amplitude with depth or alternatively with time.

Looking now to the circuit for indicating bit wear, this comprises a pair .of electrodes '.43 vand 44 ywith suitable corresponding leads .43aand144a with lead 5i having resistance 52 Vthereinbridging these electrodes. A. source vof .potentialgsuch as battery. -53 in lead 44a, permits the establishment of a' XedD. C. potential across: the resistance `52, which fixed potential is added or subtracted With respect to the pulsating D. C. output'of the full Wave rectifier 36. This potential is Vestablished only when there has been suiiicient wear of shield l5 to permit an electrical path between electrodes 43 and 44. The imposition of the fixed D. C. potential on the D. C. portion of the logging circuit will be reflected in the D. C. recorder by a fixed increase or decrease, as the case may be, in the magnitude of the recorded current. Thus, an indication that wear has occurred will be obtained without interfering with the recording of the pulsating D. C. indicative of the logging measurements being made.

A measuring sheave or pulley 45 is connected through suitable mechanical connections, represented by the shraft 46 with Selsyn generator 50, the function of which is to maintain synchronism between the pulley 45 and the recording medium 4l. The recording medium is driven byrSelsyn motor 48 which is kept in synchronism with generator 50 by conductors 4E.

A large number of methods are available for following the downward movementof the drill bit I0, but a preferred method is a wireline attached at its lower end to a traveling block which supports the drill string I2 and passed over a pulley 45 located substantially directly above the traveling block and then wound upon a drum which is provided with a spring having a strengthsuiiicient to keep the wire line is slight tension regardless of the position of traveling block. Obviously, the pulley 45 rotates in a manner dependent upon the vertical movement of the traveling block and hence of the entire drill string I2 and bit |70. I have chosen in this instance to utilize pulley 45 as the means for providing depth indications and for this purpose the Selsyn generator 50 is illustrated connected to the pulley'45. Any rotation of pulley 45 is therefore transmitted by means of generator and conductors 49 to the corresponding `Selsyn motor 48, which is preferably located a short distance away from the drilling rig, and which is utilized to drive the recording medium 4l.v

Figure 4 illustrates a drill bit and shielded electrode assembly adapted for use with the combination logging and indicating circuit schematically illustrated in Figure 3. In this embodiindicating Vcircuit on :a D. .C. zpotential. It is A'also :contemplated'that more .than oneelectrode canbe .connected to each :conductorin anyone of the .embodiments herein described. In .any event,V the logging-While-,drilling 'dataaregnota .versely '.aiecte'd fby :the `indicating `Acircuit but a "singleitrace canbe obtained .to show a conventional YAelectrical log and the Apredetermined.Lex-- tentof wear of the drill bit.

.From the aboveitwill .be apparent that 'I' have attained the objects of my invention and have provideda novel method and means `which is usefulrfor indicatingl `wear of well-'tools andwhich means :i may; be integrated with. a logging-Whiledrilling system. i

Although my invention has been described with reference to particular embodiments thereof, it should be understood that they are for illustration only. For example, it is contemplated that my method and apparatus, which have been described with particular reference to detecting the disintegration of an element, will be useful in transmitting information from any inaccessible apparatus, particularly where there is an electrical conducting fluid in the region of the inaccessible element. Therefore, the invention is not limited to the illustrated embodiment but is defined by the appended claims.

I claim:

1. A drilling assembly comprising a hollow drill stem of electrically-conducting material, a coupling of electrically-insulating material fixed to `the lower end of said drill stem, an electricallyconducting drill bit carried by said coupling, a recess in said drill bit communicating with said hollow drill'stem through a channel in said bit, said channel accommodating an insulated electrical conductor electrically connected to the lower end of said drill stem -above said coupling, an electrode in said recess connected to said electrical conductor in said channel, a plug of insulating material closing the said recess and electrically shielding the said electrode, and a surface circuit 5 including a battery, an electrical measuring instrument, and a ground electrode in series with said drill stem, electrical conductor, and shielded electrode; whereby the disintegration of the shielding plug during drilling exposes the drill bit electrode Within said recess to complete the electrical circuit so as to give a surface indication that a given extent of drill bit wear has occurred.

2. An apparatus for logging bore holes and for indicating bit wear kcomprising an alternating current generator having a constant output, a coupling transformer connected to said output, a pair ofvertically spaced logging electrodes connected to the coupling transformer whereby a fixed alternating potential is supplied across the logging electrodes, one of said electrodes being positioned within a bore hole, a fixed resistance in the circuit between the logging electrode within the bore hole and said coupling transformer.. an amplifier across said xed resistance, a fullA *i 8 wave rectier, lead's from 'saidf'amplierx tol said tr'extending"within said passage and having a rectifier, conductor means for feeding thepulsatiterminal kexposed'within said recess, a separable ing'direct current output ofthe fullwav'e rectier plug" of electrical insulating material electrically to a recording portion of the logging circuit, vsaid sealing the said recess, and an electrical circuit recording portion of the logging circuit including 5 including acurrent source, a current responsive a direct current indicator and'apotentialdivider', indicator and said conductor in series, whereby a'choke coil for protecting the D. C. recorder from wearing away of the `cutting edge to an extent A; C. current, a pair of indicating electrodes, a suchfas to removev the plug from the recess expair of electrical leads connected respectively to poses 'the terminal of the conductor for closing each of said indicating electrodes, ,.-a 'xedre- 10 the electrical circuit and producing a signal on sistance bridging said leads, a sourceof potential said indicator.

in series with said indicating electrodes-and 1 V4i.' The apparatus of claim 3 wherein the curbridging resistance, one of said leads being fixed rentlrespo'nsive indicator is a galvanometer. f to said full Wave rectifier and the other of said A EVERETT A. JOHNSON. leads being connected toA said coupling transil5 former whereby said source of potential'becomiss Y Y .REFERENCES CITED effectivewhen the circuit is closed between' the Thev following references are of record in the indicating electrodes, and any indication ofthe lgof this patent; extent of Wear is obtained 'on the'D. C. recorder without interfering with the recording of' tne'pui- 2o UNITED STATES PATENTS sating D. C. current which is indicative` of the rel.- Nl'lm'b f Name Date sistivity logging measurements in the 1ogging-cir- 2,146,357 Schweikle Feb. '7, 1939 cuit. f i 2,239,106 Krall Apr. 22, 1941 l3; An apparatus including a drillv bit having 2,249,769 LeOnaldOn J111y22, 19.41 cutting edges, a recess in one of. said edgesn kpas-y 25 2,310,611 Blondeau Feb. 9, 1943 sage extending from Within said bit and in com- 2,457,960 Walker Jan. 4, 1949 munication with said recess, an insulated-conduc- 42,468,905 v rWarren May 3, 1949 

